Orthopedic surgeons perform joint replacement surgery for patients who suffer pain and physical limitations caused by joint surfaces that have been damaged by degenerative, traumatic, or other pathologic processes. The functional outcome from these joint replacement surgeries is directly related to the degree of morbidity associated with the surgical method and the ability of the method to best restore the natural anatomy and biomechanics of the joint. Orthopedic surgeons are continually searching for ways to improve outcomes for joint replacement surgery by developing methods of less invasive surgery to limit surgical morbidity and by developing novel methods and implants to better restore the native joint anatomy.
Conventional shoulder replacement surgery has several limitations. It requires an extensive exposure that irreversibly damages the rotator cuff and still fails to gain sufficient joint access to properly restore the native anatomic relationships of both the humeral head and glenoid surfaces. Also, there remain issues with glenoid implant fixation and early loosening.
Surgical replacement of the shoulder joint requires large incisions and dislocation of the shoulder which can be detrimental to the function of the shoulder postoperatively.
One of the major technical challenges to traditional open incision shoulder arthroplasty is the requirement of surgical release of the subscapularis muscle at the front of the shoulder. Conventional methods utilize a large anterior deltopectoral exposure. The anterior humeral circumflex blood vessels are typically ligated and the anterior (subscapularis) musculotendinous unit is transected. The shoulder must then be completely dislocated both anteriorly and posteriorly to prepare the humeral and glenoid joint surfaces. This can cause excessive traction on the arm which has resulted in injury to the nerves of the brachial plexus.
The amount of time spent waiting for this muscle to heal post-operatively, typically 6 weeks, can be detrimental to the overall outcome in the long term. The literature has also demonstrated that even with perfect technical handling of this muscle that the muscle function itself is altered such that it may never return to normal. Lynch N. M., et al., Neurologic Complications After Total Shoulder Arthroplasty, J. Shoulder Elbow Surg., 1996; 5(1) at 53-61; James C. Kasper, et al., Journal of Shoulder and Elbow Surgery, July, 2008 Vol. 17, Issue 4, at 659-662; Kamal I. Bohsali, et al. Complications of Total Shoulder Arthroplasty, J. Bone Joint Surg. Am., October 2006; 88 at 2279-2292.
Additionally, if this muscle fails to heal properly, either due to biologic failure or technical failure of repair, then complications can ensue which may include instability or dislocation of the shoulder, weakness, loosening of implants, loss of function, and need for revision surgery. Bruce S. Miller, et al. Journal of Shoulder and Elbow Surgery, September 2005 Vol. 14, Issue 5, at 492-496.
With regards to shoulder replacement surgery, all conventional methods require surgical transection of a rotator cuff tendon to gain sufficient exposure of the joint surfaces of the shoulder. See U.S. Pat. No. 4,550,450, entitled, “Total Shoulder Prosthesis System,” which is incorporated herein by reference. After the joint surfaces are replaced, the rotator cuff tendon must be surgically repaired with suture material. This tenuous repair necessitates an obligatory period of approximately six weeks for the rotator cuff tendon to heal before advanced shoulder rehabilitation can be performed. This surgical transection and subsequent repair, as well as the delay in rehabilitation, hold significant consequences for the functional outcome of the shoulder replacement including permanent weakness and decreased range of motion. Miller S. L. et al., Loss of Subscapularis Function After Total Shoulder Replacement: A Seldom Recognized Problem, J. Shoulder Elbow Surg., January-February 2003, 12(1), at 29-34.
Additionally, despite the extensive exposure, conventional methods for shoulder replacement surgery still fail to properly restore the native anatomic relationships of the joint surfaces of the shoulder. Conventional methods prepare the humeral surfaces of the shoulder joint by referencing off the intramedullary axis of the humeral shaft. This poses great difficulty for the surgeon since the intramedullary axis has an inconsistent relationship to the humeral surface. The humeral joint surface also possesses a complex anatomy with significant variability which cannot be entirely restored with conventional methods and implants. There exists much variability in the humeral head neck-shaft angle, posterior and medial offset, version (rotation), height, thickness, and radius of curvature. Boileau P., et al., The Three-Dimensional Geometry of the Proximal Humerus, J. Bone Joint Surg. Br., 1997, 79B, at 857-865; Iannotti J. P., et al., The Normal Glenohumeral Relationships. An Anatomic Study of One Hundred and Forty Shoulders, J. Bone Joint Surg., 1992; 74A(4), at 491-500; McPherson E. J., et al., Anthropometric Study of Normal Glenohumeral Relationships, J. Shoulder Elbow Surg., 1997; 6, at 105-112; Soslowsky L. J., et al., Articular Geometry of the Glenohumeral Joint, Clin. Orthop., 1992, 285, at 181-190. The failure to restore the native anatomic relationships and biomechanics to the shoulder joint has proven to result in a significantly lesser functional and durable outcome. Williams G. R., et al., The Effect of Articular Malposition and Shoulder Arthroplasty on Glenohumeral Translations, Range of Motion, and Subacromial Impingement, J. Shoulder Elbow Surg., 2001; 10(5), at 399-409.
Shoulder arthritis is a debilitating problem that is treated by many orthopedic surgeons. The goals of surgery are restoration of shoulder function and decreased pain via the replacement of damaged arthritic joint surfaces with prosthetic devices that will be durable in the long term. Surfaces that are replaced include the humerus (“ball”) and the glenoid (“socket”) which is a part of the scapula bone. Michael A. Wirth, et al., J. Bone Joint Surg. Am., May, 2006, 88, at 964-973.
The primary objective of an arthroscopic approach is to spare the subscapularis muscle and the other rotator cuff muscle such that immediate and active movement of the shoulder can be achieved directly after surgery without delay to wait for healing. Additionally the risk of muscle dysfunction due to its violation at the time of surgery is avoided, and the complication subscapularis muscle detachment and the ensuing instability will be avoided, and thus patient satisfaction improved. Laurent Lafosse, et al., Primary Total Shoulder Arthroplasty Performed Entirely Thru the Rotator Interval: Technique and Minimum Two-Year Outcomes, Jun. 22, 2009, Journal of Shoulder and Elbow Surgery, November, 2009 Vol. 18, Issue 6, at 864-873.
Another current problem with shoulder replacement is that the primary cause for revision shoulder replacement surgery in long term outcome studies remains loosening of the glenoid component. Eric J. Strauss, et al., Journal of Shoulder and Elbow Surgery, September, 2009, Vol. 18, Issue 5, at 819-833. The majority of these implants have been made of high-density polyethylene, which are cemented into bone. Many have also been older generation metal-backed components which were also cemented into bone.
Additionally, the thickness of the implants causes the articulation of prosthetic implants to occur further away or laterally from the natural and native anatomy of the shoulder joint. This has been implicated in a method of loosening the glenoid component that has been referred to as the “rocking horse” effect. The lateralized position of the glenoid component allows for load to occur unevenly upon the joint and the glenoid component rocking it back and forth and causing it to separate from the bone and loosen.
As to the problem of rotator cuff (subscapularis muscle) dysfunction, rupture, or failure of repair postoperatively, modifications have been attempted to improve results which include removing the muscle with attached bone and repair of said construct at the time of surgery. Sheeraz Qureshi, et al., Subscapularis Function After Total Shoulder Replacement: Results With Lesser Tuberosity Osteotomy, Nov. 16, 2007, Journal of Shoulder and Elbow Surgery, January, 2008, Vol. 17, Issue 1, at 68-72. Other investigators have used either a subscapularis and rotator cuff sparing open approach to the shoulder or a partial release of the subscapularis with good short term results. Laurent Lafosse, et al., Primary Total Shoulder Arthroplasty Performed Entirely Thru the Rotator Interval: Technique and Minimum Two-Year Outcomes, Jun. 22, 2009, Journal of Shoulder and Elbow Surgery, November, 2009 Vol. 18, Issue 6, at 864-873; Felix A. Savoie, MD, Unpublished Internet Communication, www.vumedi.com, 2010. These are open procedures that have also been described as arthroscopically assisted for capsular release or removal of osteophytes (bone spurs).
Regarding loosening of the glenoid component, newer generation designs for open surgery show promise in early results but no long term data exists yet to show superiority over older designs. These include metal backed or hybrid components that allow bone to engage and “grow into” the component for theoretical permanent union between the two and stability. Pascal Boileau, et al., Cemented Polyethylene Versus Uncemented Metal-Backed Glenoid Components in Total Shoulder Arthroplasty A Prospective, Double-Blind, Randomized Study, Journal of Shoulder and Elbow Surgery, July, 2002, Vol. 11, Issue 4, at 351-359.
Arthroscopic options have been described in the literature which to date have been proposed as short to medium term alternatives for younger patients and potentially as a stepping stone prior to traditional open shoulder arthroplasty. Long terms outcomes at best have been described as 5-7 years. Weber et al., Arthroscopy; deBeer et al., Arthroscopy, May, 2006, Vol. 22, No. 5, at 570.el-570.el5; Burkhart, et al., Arthroscopy, September, 2007, Vol. 23, No. 9 at 1019-1022; Savoie et al., Arthroscopy, August, 2009, Vol. 25, No. 8, at 864-871. These techniques include removal of osteophytes, reshaping of humeral and glenoid bone, release of tight capsular structures, and in some cases interposition of various allograft biologic or synthetic allograft material between the glenoid and humerus to act as a cushion for the joint.